DC-DC converters use one or more switches for converting an input voltage level into an output voltage level. In buck DC-DC converters, one of the switches may be coupled to the input power supply. This switch is referred to as the high-side switch (HSS). If the high-side switch is an NMOS transistor, the voltage level at the control gate of the transistor must be greater than the input voltage level in order to turn the switch on. Such a high control voltage level is usually generated with a bootstrap circuit. Furthermore, there can be a control transistor coupled between the output node of the bootstrap circuit and the control gate of the high-side switch. This control transistor requires a complex active gate driver circuit for turning the control transistor on and off. Furthermore, the voltage levels at the drain, source and gate of the control transistor must comply with the limitations of the used technology. If the high-side switch is driven with signals of a rather high switching frequency, the timing of the signals for the transistors can be demanding.